Pupin cable for simultaneous low frequency and carrier frequency telephony



Match 6, 1934. K. KUPFMULLER PUPIN CABLE FOR SIMULTANEOUS LOW FREQUENCY AND CARRIER FREQUENCY TELEPHONY Filed May 25, 1928 "00 5'000 ao'oo Her/z a my T m L w [oug fgi zen'c y Me Cbrrecic'ny (Em w): saJor'J Patented Mar. 6, 1934 PUPIN CABLE FOR FREQUENCY AND TELEPHONY Karl Kiipfmiiller, Berlin- SIMULTANEOUS LOW CARRIER FREQUENCY Friedenau, Germany, as-

signor to Siemens & Halske, Akticngesellschaft, Siemensstadt, near Berlin, a corporation of Germany Application May 25, 1928, Serial No. 280,452 In Germany May 27, 1927 6 Claims. (01. 179-25) My invention relates to electric systems for the transmission of messages and particularly to systems employing loading coils of the Pupin type. The object of my invention is to enable a conduit or cable provided with Pupin coils to be used for two kinds of telephone messages, viz. messages of ordinary telephone or speech frequency, and messages of a frequency higher than the usual low frequency telephone messages. Hitherto lines or cables provided with Pupin coils have been suitable for the proper or distortionless transmission of telephone messages only when such messages were of one kind exclusively, that is to say, either the line was suitable for the transmission of low frequency ordinary telephone messages, or for the exclusive transmission of higher frequency (carrier frequency) telephone messages, and so far as I know, it has never been possible heretofore to transmit telephone messages of both kinds satisfactorily over the same line. The purpose of my present invention is to accomplish this desirable result of simultaneous transmission over one and the same cable orline, of both low and high frequency telephony, in the sense indicated above.

Reference is to be had to the accompanying drawing, in which Figs. 1 and 2 are diagrams illustrating two different modes of carrying out the present invention; Fig. 3 is another diagram illustrating certain conditions hereinafter referred to; Fig. 4 is a diagrammatic view of an apparatus or system embodying my present invention; and Fig. 5 is a detail of a modification.

In this invention I employ only the lower side 35 band of the modulated speech currents in the carrier frequency transmission and I am thus enabled to obtain a relatively large range of frequencies, since the carrier frequency will be substantially greater than the highest low speech 40 frequency to be transmitted. Thus, if the cut-off frequency in is taken or set at 6,000 cycles (as indicated in Figs. 1 and 2), which is a customary figure for lines having normal or relatively light loading, there will be room between such cut off frequency and the low speech frequency range N such as used for ordinary telephone messages, for a higher range of carrier speech frequency T. The line is loaded for the usual speech frequency range indicated at N, say from 300 to 2400 cycles, and without any further provision as regards loading, the same line will, if arranged according to my invention, also carry high speech frequency carrier waves of the range indicated at T, say between 2600 and 4700 cycles. This range 5 represents the lower side band of the speech carrier frequency. The carrier frequency proper is indicated at h in Fig. 1, and may he, say, 5000 cycles. The frequency it should be chosen about from 15 to 20% below the cut-off frequency in, since at higher ranges correction of the attenuation distortion can not be obtained. A still greater safeguard against such distortion may be secured by suppressing the carrier frequency, by means well-known in the art. ig. 2 illustrates the distribution of the frequency bands in this case, the only difference between Figs. 1 and 2 being that the latter omits the carrier frequency h (of 5000 cycles).

When great distances are to be covered, diffi- 1 culties arise on acount of phase distortion in the carrier frequency channel T. To overcome such difficulties, -I free said channel of distortion by phase-correcting means, in a manner which in itself is wellknown in the art. These phase- 4 correcting means may be located either at the 7 amplifying stations or exchanges, or at the ends of the line, and it will be understood that such phase-corrections may be applied only to the high speech carrier frequency channel T, without regard to the distortions present in the low frequency channel N. The phase-correcting means may consist, for instance, of distortion compensators such as shown in my United States Letters Patent No. 1,638,536 of August 9, 1927', where I employ phase-correcting networks in the form of crossed members or a combination of such members.

The separation of the carrier frequency channel T from the low frequency channel N is efiected by means of wave filters, as will be more fully explained below with reference to Fig. 4. With such filters, any phase distortion occurring in the low frequency channel N and in the high frequency range T may be compensated separately, since the phase distortion occurring in the low frequency channel will have no detrimental effect on the messages in the high frequency channel, and vice-versa. This will be understood best by reference to Fig. 3. Here the curve 1 represents the time of transit as a function of the frequency. In the carrier frequency channel T this time of transit is completed to the values indicated by the curve 2.

According to my invention, a considerable saving in equalizing or compensating means may be effected, since it is not necessary to effect equalization or compensation, with respect to the time of transit values of curve 2, throughout the entire frequency range T. Should any phase distortion occur in the low frequency channel N, 110 phase-correcting means effective on this channel alone (and having no effect on the channel T) may be provided, their action being indicated by the curve 3,1 Fig. 3.

4. Here I have indicated at S182 filters (of a type well-known in the art) for separating the paths of the messages of the frequency ranges N and T respectively. At A, I have indicated equalizing or compensating circuits, which may be of any wellknown or approved character, for instance with differential transmitter and artificial lines. At

B, I have indicated the amplifiers. In the low.

frequency portion N containing the filters $2, I have also shown, in Fig. 4, phase-correcting networks (compensators) P2, in series with said filters; similarly, phase-correcting networks P1 are shown in series with the filters S1 of the high frequency portion T. Instead of employing such compensators in series with said filters, I might use filters having phase-correcting properties, and thus dispense with separate compensators. Furthermore, I may modify the arrangement illustrated in Fig. 4 by omitting the series-connected compensators P1 P2 and inserting compensators P3 in each of the two lines or message paths; this latter feature is shown in Fig. 5, it being understood that the parts between the lines a, b of Fig. 5 are intended to be substituted for the parts between the corresponding lines of Fig. 4. Fig. 5 shows the phase-correcting means or compensators P3 adjacent to one of the amplifiers B, this being the preferred arrangement.

Fig. 4 also shows two lines or message paths, one (the upper one) for messages, both of the low frequency and of the high frequency, traveling in one direction (from left to right), and the other for messages of both kinds traveling in the opposite direction. This preferred arrangement enables me to use the same amplifiers B for messages of both frequency ranges. According to the principle explained in connection with Figs. 1 and 2, these amplifiers B should be so constructed as to neutralize the line attenuation within a frequency range of approximately 300 to 5000 cycles. It will be understood that each of the separate lines containing theamplifiers B, comprisestwo wires, so that, as stated above, the system. is a four-wire system. For the purpose of avoiding cross-talk in the case of multiple cables, it is advisable to arrange the outgoing and the incoming lines of the different messages in groups separated from each other either simply by an air gap or by static protective sheaths C (Fig. 4).

It will be understood that in my present invention, I utilize only the lower side band of the speech carrier frequency; in other words, the upper side band is suppressed, and in some cases (Fig. 2), even the carrier wave is suppressed.

The drawing indicates a cut-off frequency of the Pupin cable as 6000 cycles, which corresponds to what is termed in the art a light loading of the Pupin cable.

Various modifications may be made without departing from the nature of my invention as set forth in the. appended claims.

I claim:

1. In combination with a Pupin cable, a system for transmitting a low-frequency speechband and a carrier frequency speech-band immediately above such low-frequency band but below the cut-off frequency of the Pupin cable, said system being of the four-wire type containing two separate double lines each serving for the transmission of a low-frequency speechband in one direction only and also for the transmission of a carrier frequency speech-band in one direction only, one of the separate double lines serving for the transmission of a low-frequency speech-band in one direction and also for the transmission of a carrier frequency speech-band in the same direction, while the other double line serves for the transmission of the said low -frequency speech-band and of the said-carrier frequency speech-band in the opposite direction, the two lines which serve for transmission in opposite directions, being electrically shielded from each other.

2. In combination with a lightly-loaded longdistance Pupin cable, a system for transmitting a low-frequency speech-band and one of the side bands of a voice-modulated carrier frequency above said low-frequency band yet below the cut-off frequency of said lightly-loaded cable, the other side band of said voice-modulated carrier frequency being suppressed.

3. In combination with a lightly-loaded longdistance Pupin cable, a system for transmitting a low-frequency speech-band and one of the side bands of a voice-modulated carrier frequency above said low-frequency band yet below the cut-off frequency of said lightly-loaded cable, the other side band of said voice-modulated carrier frequency being suppressed, and means for correcting distortion in the channel of the carrier current.

4. In combination with a lightly-loaded longdistance Pupin cable, a system for transmitting a low-frequency speech-band and one of the side bands of a voice-modulated carrier frequency above said low-frequency band yet below the cut-off frequency of said lightly-loaded cable, the other'side band of said voice-modulated carrier frequency being suppressed, and meansfor correcting separately the phases in the said low-frequency speech-band and in the transmitted. side .band of the said voice-modulated carrier frequency.

5. In combination with a lightly-loaded longdistance Pupin cable including two double lines, means for producing and transmitting over said lines a low-frequency speech-band and one of the side bands of a voice-modulated carrier frequency, the other side band of said voice-modulated carrier frequency being suppressed, and said double lines being combined in such a manher as to form twospeaking connections.

6. In combination with a lightly-loaded longdistance Pupin cable including two double lines, means for producing and transmitting over said lines a low-frequency speech-band and one of the side bands of a voice-modulated carrier frequency, the other side band of said voice-modulated carrier frequency being suppressed, said double lines being combined in such a manner as to form two four-wire lines in such a manner that the respective double lines serve for transmission in opposite directions, each double line serving to transmit both a low-frequency speechband anda carrier frequency speech-band, and amplifiers in. each double line, each amplifier being effective on bothof the bands transmitted over the same double. line.

. KARL KUPFMULLER- 

